1. Field of the Invention
This invention relates to transducers for converting mechanical input signals into a corresponding electrical output signal and, more particularly, an apparatus for converting three dimensional displacements into an electrical output signal having X, Y and Z components.
2. Description of the Prior Art
A wide variety of joystick controllers having three dimensions of control and devices for converting a force vector into an electrical signal having X, Y and Z components are disclosed in the prior art. U.S. Pat. No. 3,693,425 (Starita) discloses a force measuring apparatus which includes a circular base element to which four vertically oriented fixed supports are coupled at ninety degree intervals. Each vertically oriented fixed support includes a horizontally oriented support beam and a grouping of four circumferentially positioned strain gauges. The periphery of a centrally located input device is coupled to the surrounding horizontally oriented support beams. Displacements of that input device ultimately deflects the grouping of sixteen strain gauges to generate an electrical output signal representative of the X, Y and Z components of the input displacement.
U.S. Pat. No. 4,078,226 (EerNisse) discloses a signature verification system which includes a first set of strain gauges positioned within a writing instrument and a second set of strain gauges positioned within a horizontally oriented writing platen. The writing instrument includes two parallel oriented piezoelectric transducers which are coupled to opposing sides of a ball point pen refill within the writing instrument. Deflection of the tip of the ball point pen refill deflects the two piezoelectric strain gauges in the writing instrument to generate an electrical output signal representative of the X and Y components of the force vector applied to the writing instrument. In the horizontally oriented writing platen, three spaced apart piezoelectric pressure sensors measure the Z component of the force vector applied to the writing platen. Various electronic devices process the electrical output signal from this system to produce a signal representative of the X and Y components of the force vector related to the pen which is tilted at some arbitrary angle with respect to the writing platen and also the Z component of the force normal to the platen surface. These force versus time records may then be utilized to verify whether a signature is genuine.
U.S. Pat. No. 3,998,934 (Kamphoefner) discloses a handwriting sensing and analyzing apparatus. This device includes a horizontally oriented writing platen which is coupled to an intermediate support structure by two tabs each of which includes a pair of strain gauges. The intermediate support structure is coupled to a supporting frame by an orthogonally aligned pair of tabs which include two additional pairs of strain gauges. A third grouping of strain gauges is coupled to the apparatus to measure the Z axis force components produced by the writing instrument.
U.S. Pat. No. 3,640,130 (Spescha) discloses a force measurement apparatus which includes a fixed base member and an active or movable upper member. A plurality of twelve strain gauges is coupled to electronic processing circuits which convert an input force vector into an electrical signal which is representative of the X, Y and Z components of the input force vector.
U.S. Pat. No. 4,046,005 (Goroski) discloses a three axis joystick controller. The non-movable joystick controller uses four spaced apart strain gauges to convert forces applied to the joystick into an electrical output signal representative of desired, X, Y and Z components of the control signal. The Z axis control input is created by applying a torque to the cylindrical body of the joystick controller. U.S. Pat. No. 4,217,569 (Njedly) discloses a three dimensional strain gauge transducer somewhat similar to the three axis joystick control device disclosed in the Goroski patent. The Njedly joystick controller can be deflected in two dimensions, but also generates a Z axis output signal by permitting the input shaft of the controller to be rotated.
U.S. Pat. No. 3,561,280 (MacPhee) discloses a three axis strain gauge control device which includes six strain gauges. Displacement of the flexible input shaft of the control device generates output signals representative of the desired X and Y control inputs. Vertical displacement of the control device generates the Z axis output signal by internally displacing a cantilever beam attached to the lower end of the shaft.